1. Field of the Invention
The present invention relates to an image processor for processing image data to be displayed and, more particularly, to an image processor for processing pixel data defining the intensity values of a source image.
2. Description of the Prior Art
A problem which arises in the generation and processing of images to be displayed on a visual display device or on a printer medium or the like is the physical constraints of the display device or print medium on which the generated image is to be output. Often it is not possible to display the full range of intensity values which exist in the image. What normally happens in such a case is that saturation of the image occurs in an area where the brightness is too great to be displayed. The result of this, particularly in the case of images generated by a computer modelling system, is that harsh edges will be generated where saturation occurs.
Such problems are encountered in photography where a negative film is able to resolve a greater range of brightness values than the prints made from the negative. The simple solution to this problem, which is applied in the photographic world, is to change the exposure time. A disadvantage of this process is that the picture generally becomes darker with the result that detail may be lost in some areas of the screen.
A similar approach could be applied in the case of electronically stored images, by applying a scaling factor to the image values (effectively changing the brightness) so that the range of image values can be effectively resolved on the screen. However, this would also have the effect of darkening the overall image and could result in a loss of detail in the darker areas of the image.
In photography, it is also known to selectively change the exposure time on brighter areas of the picture, without changing it on darker areas. This has the effect of reducing the overall brightness range without further darkening the darker areas. This is, however, a process which is not suitable for automation.